This disclosure relates generally to an electromagnetic tracking system that uses electromagnetic fields to determine the position and orientation of an object, and more particularly to a system and method for improving the distortion tolerance of an electromagnetic tracking system.
Electromagnetic tracking systems have been used in various industries and applications to provide position and orientation information relating to objects. For example, electromagnetic tracking systems may be useful in aviation applications, motion sensing applications, retail applications, and medical applications. In medical applications, electromagnetic tracking systems have been used to provide an operator (e.g., a physician, surgeon, or other medical practitioner) with information to assist in the precise and rapid positioning of a medical device or instrument located in or near a patient's body during image-guided surgery. An electromagnetic tracking system provides positioning and orientation information for a medical device or instrument with respect to the patient or a reference coordinate system. An electromagnetic tracking system provides intraoperative tracking of the precise location of a medical device or instrument in relation to multidimensional images of a patient's anatomy.
An electromagnetic tracking system uses visualization tools to provide a medical practitioner with co-registered views of a graphical representation of the medical device or instrument with pre-operative or intraoperative images of the patient's anatomy. In other words, an electromagnetic tracking system allows a medical practitioner to visualize the patient's anatomy and track the position and orientation of a medical device or instrument with respect to the patient's anatomy. As the medical device or instrument is positioned with respect to the patient's anatomy, the displayed image is continuously updated to reflect the real-time position and orientation of the medical device or instrument. The combination of the image and the representation of the tracked medical device or instrument provide position and orientation information that allows a medical practitioner to manipulate a medical device or instrument to a desired location with an accurate position and orientation.
Generally, electromagnetic tracking systems include electromagnetic transmitters and electromagnetic receivers with at least one coil or a coil array. An alternating drive current signal is provided to each coil in the electromagnetic transmitter, generating an electromagnetic field being emitted from each coil of the electromagnetic transmitter. The electromagnetic field generated by each coil in the electromagnetic transmitter induce a voltage in each coil of the electromagnetic receiver. These voltages are indicative of the mutual inductances between the coils of the electromagnetic transmitter and the coils of the electromagnetic receiver. These voltages and mutual inductances are sent to a computer for processing. The computer uses these measured voltages and mutual inductances to calculate the position and orientation of the coils of the electromagnetic transmitter relative to the coils of the electromagnetic receiver, or the coils of the electromagnetic receiver relative to the coils of the electromagnetic transmitter, including six degrees of freedom (x, y, and z measurements, as well as roll, pitch and yaw angles).
Preferably, the mutual inductances between coils of the electromagnetic transmitter and the electromagnetic receiver may be measured without inaccuracies. However, electromagnetic tracking systems are known to suffer from accuracy degradation due to electromagnetic field distortion caused by the presence of an uncharacterized metal distorter within the tracking volume or electromagnetic fields of the electromagnetic tracking system. The presence of an uncharacterized metal distorter within the tracking volume of the electromagnetic tracking system may create distortion of the electromagnetic fields of the electromagnetic tracking system. This distortion may cause inaccuracies in tracking the position and orientation of medical devices and instruments by causing inaccuracies in position and orientation calculations of the coils of the electromagnetic transmitter relative to the coils of the electromagnetic receiver, or the coils of the electromagnetic receiver relative to the coils of the electromagnetic transmitter.
Therefore, there is a need for a system and method for improving the distortion tolerance of an electromagnetic tracking system, and minimizing the effect of distortion on position and orientation calculations performed by the electromagnetic tracking system.